1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a dipole antenna for a wireless communication device.
2. Description of the Prior Art
A dipole antenna is a straight electrical conductor measuring ½ wavelength from end to end and connected at the center to a radio frequency (RF) feed line. This antenna, also called a doublet, is one of the simplest types of antenna, and constitutes the main RF radiating and receiving element in various sophisticated types of antenna. The dipole is inherently a balanced antenna, because it is bilaterally symmetrical. According to that, the dipole antenna exhibits a symmetric radiation pattern. A symmetric radiation pattern provides uniform gain in 360 degrees, thereby allowing equally effective communication in all directions. However, the radiation distance is limited by power supplied to the antenna, so if we want to realize far-distance communication in all direction, adding power supply is needed. Base station antennas used in wireless communication systems adopt dipole antennas mostly along with high power transmitter.
In additional to be used in base station, dipole antennas can also be used in other fields. Especially in these years, with the development of wireless local area network (WLAN), dipole antenna finds its new application. It is well known that the efficient radiating radius of WLAN covers the range of 30 to 300 meters in which an omni-direction antenna (such as dipole antenna) will be an optional choice to engineers. U.S. Pub. No. 2004/0080464 published to Suganthan et al. on Apr. 29, 2004 and entitled “Dual band single feed dipole antenna and method of making the same” discloses a dual band single center feed dipole providing a single band dipole antenna and loading the single band dipole antenna with two open circuit stubs or arms forming a second half-wave dipole. The antenna is printed antenna structure, which can be integrated with other microelectronic devices on a substrate. Here, another dipole antenna formed of metallic sheets is provided, which has a compact construction and is used for industrial scientific medical (“ISM”) band operation covering, for example, frequency range of 2.4–2.5 GHz and 5.15–5.35 GHz.